The polyphenylene oxide resins are a family of engineering thermoplastics that are well known to the polymer art. The polyphenylene oxides may be made by a variety of catalytic and non-catalytic processes from the corresponding phenols or reactive derivatives thereof. By way of illustration, certain of the polyphenylene oxides are disclosed in U.S. Pat. Nos. 3,306,874; 3,306,875; 3,257,357; and 3,257,358. In accordance with the prior art the polyphenylene oxides can be prepared by an oxidative coupling reaction comprising passing an oxygen-containing gas through a reaction solution of a phenol and a metal-amine complex catalyst. U.S. Pat. No. 3,356,761 discloses polyphenylene oxide resins prepared by dissolving a polyphenylene oxide in styrene monomer and the styrene monomer subsequently polymerized into polystyrene to produce a mixture of polyphenylene oxide and polystyrene, i.e. a polyphenylene oxide resin. U.S. Pat. Nos. 3,373,226 and 3,383,435 disclose mixtures of polyphenylene oxide and a styrene resin.
Blending of polyphenylene oxide, or polyphenylene oxide resins, and conjugated dienemonovinylarene block copolymers has been observed previously to lead to compositions having useful properties. For example, the impact strength of polyphenylene oxide resin can be significantly increased by the addition of a minor amount of a conjugated diene-monovinylarene teleblock copolymer, whereas the addition of a minor amount of a polyphenylene oxide resin to a conjugated diene-monovinylarene copolymer results in improved high temperature properties as well as improved tear and abrasion resistance.
Mechanical blending of a polyphenylene oxide and conjugated diene-homopolymers or copolymers results in blends having less than optimum physical properties. This is due to the requirement that mechanical blending to give a homogeneous blend must be conducted at temperatures above the glass transition temperature of the polyphenylene oxide (ca. 220.degree. C.), which is too high for processing unsaturated conjugated diene-homopolymers or copolymers without serious degradation.
Solution blending of polyphenylene oxide and conjugated diene homopolymers or copolymers requires use of a solvent system which typically contains at least 10 weight percent, preferably greater than 20 weight percent, aromatic hydrocarbon solvent due to the low solubility of polyphenylene oxide in paraffinic or cycloparaffinic solvents. Although solution blending with a partially or totally aromatic solvent system does give a blended composition having good physical properties, solution blending of large samples of polymers is time consuming and expensive in view of the large quantities of solvent required and the current high prices of hydrocarbons, especially aromatic hydrocarbons.